The overall goal of this proposal is to elucidate the molecular mechanism of prevention of cardiomyocyte death mediated by the B-Raf kinase. In recent studies, activation of ERK kinases by MEK1 has been reported to partially block hypoxia/reoxygenation-induced cardiac apoptosis. Our preliminary data demonstrate that overexpression of B-Raf, an upstream regulator of MEK1, prevents apoptosis and induces hypertrophy both in neonatal and adult cardiac myocytes. Interestingly, we found that B-Raf does not require MEK1 activity to promote cell survival, whereas MEK appears to be essential for the hypertrophy response. We will therefore analyze the B-Raf-mediated prevention of cardiomyocyte death by investigating MEK1-dependent as well as independent survival signals. Since B-Raf simultaneously activates pathways that may be responsible for survival as well as hypertrophy, we will attempt to dissect these pathways by analyzing their downstream targets. Our studies will provide the first systematic analysis of survival signals mediated by the Raf pathway in cardiac myocytes. The proposed experiments will establish whether heart-specific overexpression of B-Raf can provide the basis for an interventional therapy of ischemic heart diseases by preventing cell loss. [unreadable] [unreadable] Our studies will proceed according to the following specific aims: [unreadable] 1) To determine the effect of B-Raf overexpression on hypoxia/reoxygenation-induced apoptosis and necrosis in primary cardiomyocytes. We will also test the hypothesis that a mutant B-Raf defective in MEK binding recapitulates the effect of the wild-type kinase. [unreadable] 2) To elucidate the molecular mechanism of B-Raf-dependent cell survival. We will analyze the role of potential targets of the B-Raf pathway in cell death prevention, in particular the inhibitor of apoptosis proteins (lAPs) and members of the Bcl-2 family. [unreadable] 3) To identify downstream components of the B-Raf pathway that specifically transmit hypertrophy signals. This might allow us to dissect survival and hypertrophy signals mediated by the B-Raf kinase cascade. [unreadable] [unreadable]